Polarizing plates are used in image displays (particularly, liquid crystal displays). To provide bright images with high color reproducibility, polarizing plates are required to have both high transmittance and high degree of polarization. Such polarizing plates are produced with a laminate including a polarizer and a transparent protective film bonded to one or both sides of the polarizer with an adhesive. The transparent protective film is produced with triacetylcellulose with high water-vapor permeability, or the like.
Polarizers are conventionally produced by orienting a dichroic substance such as dichroic iodine or a dichroic dye in a polyvinyl alcohol film. Specifically, polarizers are produced by subjecting a polyvinyl alcohol film being fed from a raw material roll to swelling, dyeing, crosslinking, stretching, washing with water, drying, and so on (Patent Literature 1).
The above process is performed using a roll of a polyvinyl alcohol film, and therefore, as a result of taking into account the handleability of the film and so on, there is a limit to the reduction in the thickness of the resulting polarizer. Therefore, the thickness of the polarizer obtained by the above process is generally more than 30 μm. However, as the thickness of the polarizer increases, the contraction stress of the polarizer or the polarizing plate generated therewith increases, which causes a problem in which when these are attached to form an image display such as a liquid crystal display, curling occurs to cause light leaks. The problem of such curling of the polarizing plate becomes significant, when water enters and leaves the polarizer under a humidified environment. On the other hand, the polyvinyl alcohol film from the material roll is a thin film with a thickness of about 30 μm, which also causes a problem with productivity, such as breaking of the film by a stretching process.
Concerning the problem of curling under a humidified environment, it is known that curling can be suppressed when the polarizer is entirely covered with a transparent protective film with low water-vapor permeability so that water can be inhibited from entering or leaving the polarizer under a humidified environment (Patent Literatures 2 and 3). However, even when such a transparent protective film with low water-vapor permeability is used, the entry of water from the side of the polarizing plate cannot be sufficiently suppressed. In addition, when a typical polarizing plate having transparent protective films placed on both sides is formed using transparent protective films with low water-vapor permeability, the process of forming the polarizing plate needs to include removing water from the polarizer and then bonding the transparent protective films to the polarizer. Therefore, when transparent protective films with low water-vapor permeability are used, it takes time to remove water, which is not preferred in view of productivity.    Patent Literature 1: JP-A No. 2004-341515    Patent Literature 2: JP-A No. 2002-052227    Patent Literature 3: JP-A No. 2004-090546